We plan to extend our studies of the ionic strength dependence of flavodoxin electron transfer reactions to include other flavodoxins (to test the generality of our conclusions), dichloroflavin analog protins (these are of interest because we are able to separate the rate constants for complex formation and electron transfer, which are inaccessible with the normal flavodoxin) and reactions of the fully-reduced protein (to see if ionic strength effects depend on oxidation state and also because many of the reactions of this species are too fast to measure at high ionic strength but should be measurable at low ionic strength. We also plan to continue our work on the flavin-cytochrome c-cytochrome oxidase system. Of particular interest are investigations of ionic strength dependence to examine charge interactions, of cytochrome c concentration dependence (to examine the kinetic effects of occupation of both the high affinity and low affinity binding sites on the oxidase), of dependence on the initial state of reduction of the oxidase (to examine the rates of entry of electrons into the various redox sites, i.e. a, a3 and copper), and of the effects of CO liganding of the oxidase (which changes the redox potentials of the various sites.